1. Field of the Invention
This invention relates to a graded index lens array for use as imaging elements in copying machines, facsimile equipment, CRT (cathode ray tube) printers, LED (high-density light-emitting diode) printers, LCD (liquid crystal) printers and similar equipment.
2. Description of the Prior Art
As illustrated in FIG. 4, a graded index lens array 1 for use as an imaging element in copying machines and similar equipment is integrally formed of (a) a pair of parallel resin plates 4 and 4', (b) a plurality of elongated, columnar graded index lenses 2 arranged in parallel and disposed between the resin plates, (c) a resin adhesive 5 filling the spaces between adjacent graded index lenses 2, and (d) a pair of spacers 3 and 3+ disposed at both lateral ends.
In the past, graded index lenses made of inorganic glass have primarily been used. However, graded index-lenses made of synthetic resins have several advantages over those made of inorganic glass, in that they are light in weight, have good impact resistance, can be manufactured at low cost, and can be worked easily. Accordingly, the use of graded index lenses made of synthetic resins are now increasing steadily.
Nevertheless, graded index lenses made of synthetic resins are disadvantageous in that their low hardness makes it difficult to polish their end surfaces (optical surfaces) satisfactorily. Moreover, owing to insufficient abrasion resistance, their surfaces tend to be damaged by contact with other objects, impact, scratches and dust wiping as encountered when the lens array is mounted in equipment or used for the intended purpose. This may cause a loss in resolution and prevent the lens array from forming an accurate image on the focal plane.